NFL player Colin Kaepernick refusal to stand during the playing of the national anthem a few weeks has helped ignite a collective movement in solidarity demonstrations within the NFL to raise awareness on racial inequality and police misconduct in America.

Weeks after San Francisco 49er Colin Kaepernick used the national anthem to protest social inequality, NFL players from around the league got political on Sunday, the 15-year anniversary of the Sept. 11, 2001 terrorist attacks.

Players from the Seattle Seahawks joined arms while standing during the national anthem. Several players from the opposing Miami Dolphins kneeled, as the Denver Broncos’ Brandon Marshall had done on Thursday.

USA TODAY SPORTS / REUTERS Seattle Seahawks join arms during the national anthem before their game against the Miami Dolphins.

KANSAS CITY STAR VIA GETTY IMAGES Kansas City Chiefs defensive back Marcus Peters raises his fist in the air as the National Anthem plays before Sunday’s football game against the San Diego Chargers.

New England Patriots Martellus Bennett and Devin McCourty both raised their fists for the anthem ahead of Sunday’s late game against the Arizona Cardinals, as several Tennessee Titans had earlier.

The demonstrations were sparked by San Francisco’s quarterback Colin Kaepernick, who opted to sit during the national anthem in protest of the mistreatment of people of color in the U.S., causing an uproar.

“I am not going to stand up to show pride in a flag for a country that oppresses black people and people of color,” Kaepernick had told NFL.com’s Steve Wyche. “To me, this is bigger than football, and it would be selfish on my part to look the other way. There are bodies in the street and people getting paid leave and getting away with murder.”